An AC power cord can be serviced with the server running. See AC Input Filter and AC Power Cord for the location of AC power cords.
Caution - You can replace an AC power cord while the server is powered on. However, to minimize any potential risk of damage to equipment or personnel, shut down and power off the server before replacing an AC power cord.
Note - Working conditions vary from site to site. Arrange with the customer's facilities department to schedule time to work on the server and prevent unexpected complications.